This invention relates to the treatment of soil to improve its characteristics for growing vegetation and it relates more particularly to the treatment of soil that has been contaminated by chemicals such as herbicides and other pesticides.
In my co-pending applications referred to above, the treatment of soil to improve its properties is described including buffering plant roots from harmful, toxic levels of chemicals and/or elements and degrading of harmful chemicals in soil.
This invention is particularly concerned with the detoxification of soil that has become contaminated by chemicals that have been applied directly to the soil, for example as a herbicide, or indirectly as by drainage of water or moisture from plants that have been treated with a chemical; also indirectly by the decay of plants that have been treated by chemicals and the mixing of the products of decay with the soil.
This invention is also concerned with the treatment of contaminated soil generally including the treatment of landfills and other soil which has become contaminated with toxic chemicals of various types which are organic in nature and it may have application to treatment of soil contaminated by metals.
The contamination of soil by chemicals applied to the soil directly or indirectly is a serious problem owing to the persistence of such chemicals in the soil which render it unfit for the raising of crops or of lesser use, and also the growth of other vegetation.
Heretofore soil contaminated by toxic chemicals has been detoxified, at least to some extent, by pH effects and hydrolysis, by photochemical effects and by chemical reactions. Residual pesticides have been degraded by unassisted microbiota, either added as such or naturally present in soil.
Such methods have been undependable and have not had consistent success.
It is an object of the invention to provide improvements in the detoxification of contaminated soil.
It is a particular object of the invention to provide a method, and a composition for practice of the method, which are superior to methods and compositions used heretofore and which have one or more of the advantages of economy, speed of results, and a wide spectrum of applications to toxicants.
The above and other objects will be apparent from the ensuing description and the appended claims.
In accordance with the present invention soil contaminated with a chemical is treated with a nutrient material which will cause proliferation of micro-organisms that degrade the chemical into non-toxic products.
This may be done after the contaminating chemical has had its intended effect, for example as a herbicide, to rid the soil of residues of the chemical; or the nutrient material may be applied to the soil before application of the toxic chemical to the soil, or at the time of application or shortly after application of the chemical to the soil. Where the nutrient material is applied at an early stage, that is before the chemical has had its intended effect, care should be taken to avoid or to minimize interference of the nutrient material with the intended action of the chemical. Further, the effect of the nutrient material, through the medium of the micro-organisms proliferated by its presence, may act upon and further degrade an intermediate degradation product of the added chemical.
The nutrient material may be added with or without added micro-organisms. That is, the nutrient material may be added alone to proliferate microbiota already in the soil, or micro-organisms may be added to, or along with the nutrient material.
The nutrient material may be any plant nutrient capable of causing proliferation of the desired micro-organisms but it is preferably a balanced material such as that described in the examples below which include as the major component (other than water) a carbon skeleton/energy component, a macronutrient component including a source of nitrogen and a micro-nutrient component and preferably also a complexing agent such as an alginate, a lignosulfonate, etc. Preferably the nutrient material also contains a vitamin/cofactor component.
The nutrient material may be applied in various ways, for example by adding it to irrigation water or by sprinkling or spraying it onto the soil or as a dust or granular material which is mixed with the soil, also in the form of a suspension in water.
Although the invention is described primarily with respect to toxic chemicals such as pesticides, it is applicable to the degradation of organic materials generally, for example waste materials generally, examples being automobile tires that have been finely shredded and mixed with soil.